G.f. satisfies: A(x) = x^2 - x + Series_Reversion(x - x*A(x)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =11a(5) =35a(6) =125a(7) =445a(8) =1699a(9) =6668a(10) =26935a(11) =112111a(12) =476674a(13) =2072146a(14) =9182141a(15) =41406119a(16) =189830984a(17) =883549848a(18) =4171598085a(19) =19962224926a(20) =96746007976a(21) =474586282085